1. Field of the Invention
This invention relates to a resin-sealing apparatus for sealing electronic parts such as semiconductor elements with resin.
2. Description of the Prior Art
Heretofore, for example, in the case that electronic parts such as highly integrated semiconductor elements are resin-sealed, an apparatus that is operated as described herein under has been used. In detail, electronic parts are placed at the predetermined position in a plurality of cavities formed in a mold unit comprising a movable top mold and a fixed bottom mold, resin tablets are melted in a common pot, the molten resin is extruded and injected by a plunger into the cavities through runners and gates that communicate to the pot to thereby cover and seal the electronic parts in the predetermined configuration with resin.
In the case of a resin-sealing apparatus having the structure as described hereinabove, because the cull is inevitably formed in the pot and runners, sealing resin that is trapped in the runners and call is wasted.
To improve such a resin-sealing apparatus, the inventors of the present invention proposed a resin-sealing apparatus disclosed in Japanese Published Unexamined Patent Application No. Hei 10-119082. In detail, the resin-sealing apparatus has cavities between a movable top mold and a fixed bottom mold into which sealing resin is injected for molding and the molded products are ejected out by means of an ejector pin, wherein sealing resin is inserted into an ejector guide passage of the ejector pin and heated and molten sealing resin is injected into the cavities by means of the ejector pin.
However, in the case of the resin-sealing apparatus of this type, because resin is injected into the cavities by means of the ejector guide passage and the ejector pin, the resin-sealing apparatus is disadvantageous in that (1) the durability of the mold unit becomes poor and the maintenance cost becomes high, (2) an ejector pin cannot be slid smoothly in an ejector guide passage if the thickness of the ejector pin is not thin to some degree, (3) a high pressure and a long injection time are required to inject molten resin into the cavities if the thickness of an ejector pin is thin, (4) molten resin penetrates into a gap between the ejector pin and the ejector guide passage and the ejector pin cannot be moved when the penetrated resin hardens, (5) molten resin flows into the cavities not smoothly because the ejector guide has its opening on the peripheral portion of the cavity surface and not always around the central portion of the cavity surface to thereby generate voids, and (6) injection speed of sealing resin cannot be controlled.
The present invention has been accomplished to solve the above-mentioned problems, it is the object of the present invention to provide a resin-sealing apparatus that is operated with a low pressure and a low clamping force and that is capable of shortening molding time, reducing required resin quantity, and molding without void.
According to one example of the present invention, a resin-sealing apparatus in which a resin injection inlet of a pot opens directly to a cavity of a mold unit and a plunger for injecting molten resin in the pot in to the cavity is disposed slidably and airtightly with the inside wall of the pot is provided.
According to another example of the present invention, a resin-sealing apparatus in which a plurality of cavities are formed on the mold unit, a resin injection inlet of the pot is opens to each cavity, and a pair of a pot and a plunger are disposed for each cavity is provided.
According to further another example of the present invention, a resin-sealing apparatus in which a resin injection inlet of the pot opens to the cavity surface center of the cavity of the mold unit is provided.
According to yet another example of the present invention, a resin-sealing apparatus having a pushing speed controller for controlling the pushing speed of the plunger for injecting molten resin into the cavity is provided.
Therefore, according to one example, the opening of the resin injection inlet of the pot can be formed large up to the range allowable for the area of the cavity surface, and as the result because resin in the shape of thin tablet having a large diameter that is favorable for melting resin can be used, the resin is melted at a low pressure, the melting time is shortened, and the charging speed can be faster.
Because the opening of the resin injection inlet is wide, molten resin is injected into the cavity smoothly, and because resin is charged with a low pressure, a low clamping force for clamping the top mold and the bottom mold is sufficient for molding.
According to another example, a plurality of target products to be molded are resin-sealed simultaneously.
According to further another example, molten resin is injected from the center of the cavity surface, the injected molten resin flows from the center toward periphery, air trapped in the cavity is excluded from the cavity, and thus void generation is prevented.
According to yet another example, the pushing force and pushing speed of the plunger are controlled finely depending on the cavity volume, the size of a target product to be sealed, and type of sealing resin.